Currently under research and development are processing methods for improvement in density and miniaturization in production of ULSI semiconductor devices. One of the methods, chemical mechanical polishing (CMP) technology is now a technology essential in production of semiconductor devices, for example, for smoothening of an interlayer dielectric, forming a shallow trench device isolation, and forming plugged and embedded metal wiring.
In conventional production of semiconductor devices, inorganic insulation film layers such as a silicon oxide insulation film are formed by methods such as plasma CVD and low-pressure CVD. Polishing slurries of fumed silica are commonly studied as a chemical mechanical polishing slurry for use in smoothening of the inorganic insulation film layer. The fumed silica polishing slurries are produced by grain growth, for example, by oxidative thermolysis of tetrachlorosilane and subsequent pH adjustment. However, such an polishing slurry still has a problem that the polishing speed is lower.
Shallow trench isolation has been used for isolation of devices in an integrated circuit in the generation of a design rule of 0.25 μm or later. In the shallow trench isolation, CMP is used for removal of excessive silicon oxide films formed on a substrate and a stopper film smaller in polishing speed is formed under the silicon oxide film for termination of polishing. For example, silicon nitride is used for the stopper film, and the difference in polishing speed between the silicon oxide film and the stopper film is preferably greater. Conventional colloidal silica-based polishing slurries have a smaller polishing speed ratio between the silicon oxide film and the stopper film at approximately 3, and thus, did not have properties practically usable for shallow trench isolation.
On the other hand, cerium oxide polishing slurries have been used as polishing slurries for glass surface such as of a photomask and lens. Cerium oxide particles are softer than silica or alumina particles, less likely to cause scratching on the polishing surface and thus, useful for finishing mirror-surface polishing. The particles also have an advantage that the polishing speed therewith is faster than that of silica polishing slurries. Recently, CMP polishing slurries for semiconductor processing, containing a high-purity cerium oxide abrasive have been used. Such methods are described, for example, in Japanese Patent Application Laid-Open No. 10-106994.
Also known is a fact that an additive is added for control of the polishing speed with a cerium oxide polishing solution and for improvement in global smoothness. Such methods are described, for example, in Japanese Patent Application Laid-Open No. 8-22970.